1. Field of the Invention
This invention relates to integrators, and more specifically to compensating integrators.
2. Description of the Prior Art
Integrating circuits are employed in many electronic applications, such as, for example, CT scanners. In CT scanners, one or more X-ray sources are employed with one or more detectors. An integrating circuit is connected to the output of a detector to generate a usable signal.
A problem exists, however, in that even when no X-rays are applied to the detector, it still produces an output signal. This effect introduces errors in the output of the integrator. In other integrator applications, unwanted input currents may also adversely affect the integration operation.
A solution to this problem is taught in U.S. Pat. No. 4,163,947 to Weedon. In this patent, during an autozeroing mode, an integrating capacitor is disconnected from an integrating amplifier. Then the output of the amplifier is employed to charge an error capacitor to a value related to input current errors. The voltage across the capacitor is applied to an amplifier which generates an error current provided to the input of the integrating amplifier during integration to compensate for unwanted input currents.
However, problems also exist with the Weedon circuit. For example, the circuitry is more complex, requiring an additional amplifier as compared to a conventional integrating circuit, thus increasing cost significantly. Also, if the amplifier has a high gain, the range of input currents that may be corrected for is limited.